Lord Ashdown, the former Liberal Democrat leader, claimed today that any delay over the decision to replace the Trident nuclear deterrent would be down to his party's "strong influence" within the coalition government.

The Lib Dems have seized on media reports that a final decision on the like-for-like replacement of the nuclear deterrent may be shelved until after the 2015 general election to stress the party's influence in government.

Nick Harvey, a Lib Dem armed forces minister, told the Commons last week that delaying the final spending decision on Trident by a few months "would not make any difference" to its cost. But he insisted there was "no suggestion" of putting off the decision to replace the nuclear deterrent.

However, comments made by senior Lib Dem figures who oppose the replacement of Trident, suggest they believe the issue will be kicked into the long grass.

Clegg fuelled speculation by giving the impression yesterday that the Liberal Democrats were still making the case in Whitehall for "alternatives" to the weapons system.

Lynne Featherstone, a junior Home Office minister, told delegates last night at a fringe event at the party's annual conference in Liverpool that Lib Dem coalition ministers had ensured the renewal of Trident was "no longer a certainty".

Ashdown also appeared to suggest that the delay would be a matter of years not months, as he cited the sway and "strong influence" that the party could bring to bear inside government.

Ashdown told BBC Radio 4's Today programme that a delay on a like-for-like replacement for Trident would give an opportunity to reopen a "more rational" debate on the future of the deterrent.

"It gives us space for that to be considered in a more rational fashion," he said. "I think that is a consequence of the Liberal Democrats' influence in government and I think that is a good thing."

The delay was something the Lib Dems had always believed they could achieve, he added.

"We have always said that we didn't have to take this decision until about 2014. The fact we are going to do that now gives us a chance to have a more rational discussion about this, a good thing in my view and the result of the Liberal Democrat influence in this government."

But Liam Fox, the defence secretary, is refusing to accept anything other than a minor delay in replacing Trident, government sources told the Guardian.

In a move that threatens a row with Clegg and the Treasury, Fox is telling cabinet colleagues that replacing the four Vanguard nuclear submarines can only be delayed by four to six months.

Ashdown said he could see no circumstances in the future "where you may decide to replace Trident with a like-for-like replacement".

"That is not to say that Britain does not need an independent nuclear deterrent. It does. It's merely to say that in the present strategic circumstances there are better ways of fulfilling that need."

Delegates at the Lib Dem conference have prioritised an emergency motion for debate on Wednesday that makes the case for a full review of the alternatives to a like-for-like replacement of Trident in the current strategic defence and security review (SDSR).

The motion also stipulates that the review makes explicit the "opportunity cost" of Trident replacement in terms of cuts to troop numbers and equipment programmes.

Simon Hughes, the deputy Lib Dem leader, insisted today that what his party's conference decided this week could influence government policy.

Hughes told BBC Radio 4's Today programme: "For the first time ever, motions passed at our conference are relevant in influencing our party in government."

He added: "We can stop things happening, because this is not a government where you have a second, smaller partner looking after a bit [of it] – this is a government where all the decisions are shared."